DEBOGAS · Dilute Bose Gases at Positive Temperature

The experimental realisation of Bose-Einstein condensation (BEC) in trapped alkali gases in 1995 triggered numerous mathematical investigations of the properties of dilute Bose gases. For the mathematical description of these experiments the Gross—Pitaevskii (GP) limit is relevant. In the past two decades there has been a substantial progress in the understanding of ground state properties of Bose gases in the GP limit, culminating in the recent rigorous justification of Bogoliubov’s theory for the ground state energy and for low lying excitations. Except for a recent contribution of me and my co-authors [1], the highly relevant GP limit at positive temperature has not been considered so far. The aim of the proposed project is to develop new mathematical tools to study dilute Bose gases at positive temperature. This will be done from two points of view: Thermodynamics and Dynamics. More precisely, in the first part of the project I plan to prove refined estimates (w.r.t. [1]) for the free energy in the GP limit which would yield a better understanding of how interactions affect the thermodynamic properties of such systems. In the second part I will investigate the dynamics of positive temperature states after the trapping potential will have been switched off and prove that a certain structure of the 1—pdm is stable under time evolution. Apart from asking two highly relevant questions in modern mathematical physics, the project is also interesting from a physics point of view since it would justify two frequently used approximations in the physics literature. [1] A. Deuchert, R. Seiringer, J. Yngvason, Bose-Einstein Condensation in a Dilute, Trapped Gas at Positive Temperaturre, Commun. Math. Phys. (2018). https://doi.org/10.1007/s00220-018-3239-0